Method of making fluffy, hydrated calcium sulphate



Patented Sept. 12, 1933 EATES METI-Ioi) OF MAKING FLUFF-Y, HYDRATEDGALCIUM1 SULPHATE v Walter fiogeiMacintire, Knoxville, andThomas iBarnes Stansel; Mascot Tenn, ass ignors to American Zinc, Lead &Sm'elting Company,

St. Louis, M0,; a corporation of Maine No Drawing. Ap l cation February.1 se ria1- o.59i,4 ic. I a V l'8claiins." (or 23 -422) This inventionrelates toia process of obtaining a finely divided flufly type ofhydrated calcium sulphate and the product of such process,- whichproduct is a special type of pulverulent, crystal line calciums'ulphateand is' peculiarly usefulfor usually discarded aswaste product..According to the present invention, however, insteadoi adding sulphuricacid to the dolomite, we reversethe procedure, 1. eLjwe add the dolomitein a finely divided condition to a hot suIphuric-acid Water solution ofknown concentration and controlled temperature,- the finely divideddolomite being added in fr'acti'onsof thetotal amount added, and afterthe dolomite has been added we add successive amounts of water andmaintain the tempera.-

ture control and dispersal of the solid inthe gasimpregnated mixture,with the resultant production of hydrated'calcium sulphate of exceedingfineness, minimum density and of a fibrous, crystalline structure. Thischaracteristic structure facilitates and expedites thefilti'ation of themagnesium sulphate solution.

In carrying out the process; adefinite quantity of sulphuricacidisdiluted to a prescribed volume, and an amount of finely divided dolomite(slightly less than chemical equivalence of the sulphuric acid) isthenintroduced by'progressive additions of fractions of the totalcharge. Preferably the containers areinsulat'ed to the end that thedesired minimum temperature of reaction heat of approximately C. may bemaintained. After the complete charge of'dolomite has been introduced,successive additions of water, with gentle agitation, are used,jthe"amount of water added beingsufficient to maintain a uniform pastymass until the reactions of hydration and complete chemical evolutionofcarbon dioxidehave ensued. The additions" of water a are discontinuedwhen observations between :a'gitations show. that :the mass iscontracting slightly-sumcientlyteshow a definite layer of clearsupernatant iliquidn A period of approximately forty-five minutes afterthe last dolomite addition .isre'quirejdto efiect this result.Thecontainer may be open, or it may be closed to permitt theby-productrecovery of carbon dioxide; The finely divided'rhydratedcalcium sulphate is then filtered from the solution and washed free ofmagnesium sulphate and perinittedto dry spontaneouslywith good ventila'tion and conducive temperature; or it may be driedin anyof-theconventional drying devices at a temperaturebelmv-ti) C1 Thedriedmaterial thus obtained is not only superior=to the mass offinely-divided ground mineralasfan insulating material, but it may'a1so:= be transformed into plaster ''of' Paris by the commonly"practiced .method of heating in kettles at the temperature and for theperiod required to :drive ioff approxiimat'ely three-fourthsof itscrystalline water;

Whilei'orthe purpose of describingthe'inveni tion'we shall referspecifically to ad'olomite limestone of approximately 52% CaCOsand 37 7MgCOs content, it is to beexpressly understood thattheinve'ntion is notlimited toithi's specific form oilimestoneandthe amountof H2SO4'i1Sedwill be governed by the chemical'ly d'etermined neutralizing value. ofthe limestone,:the amount of H2804 used being preferably-iarislightexcess over the theoreticalrequirementsforithe complete disintegrationof the particular limestone ernployledfl The amount of H2804 will vary,oi= course,

with the purityand iCa-l-Mg ratio content of the rocks. 'The specificform of dolomite or other methodspursued; hereinaitertreferred to,carries about 10% quartz (-sand);. 'Notwithstanding jthe' .As a specificmaple-Ea the practice (if the process; of this invention twertake 55 cc.of 1.84

then add led-grams. of .finelywground (minus-' loo-mesh) Mascot;dolomite in; progressive :fractionsrofifrom one-,sixthto one-tenth ofthe total dolomitcadded, and intermittently gently stir the-amassPreferably at =period'of approximately ten minutesensues-between"thefirst and the. final, fractions iofuthe, dolomite- It will be understoodthat slight-variations the magni tudeof the airactions; 101E the addeddolomite are not material; y

limestone referred toxin theexample ofi 'the specific gIaVitYmI'I2SO4and add thisrto l65 cc. of water and thoroughly mix the same. To this wea; After the'finallfraction dolomite been a V added; wateris added intenconsecutive portions oiil!) cc. each,;these additions; extendingover aperiod oi"approximatelyforty-five minutes. The

mixture: is v gently stirred after each addition of water niter aperiod-,offrom fiiteen to fortyfive minutes, subsequent/to the additiono fthet'l'm I last 10 cc; of water, the magnesium sulphat solu tion isfiltered and the calcium sulphate residue is washed.

The'product is readily filtered out by suction, andthe filteredandwashed product is then dried at a temperature below 89 -C.,-andpreferably screened through a 20 mesh sieve to disintegrateany lumps.The resultant product'is a volumi material native to the dolomite orother. limestone employed. It will be understood, of course,

that the containers employed are made of or lined with any suitable acidresistant material] that will stand up against both chemical reactionand abrasion. If the reactions involved be brought about in a'closedsystem, the'evolved 002 may be conserved, otherwise theprocess'maybe'carried outin open vessels. I

invention is a complete inversion ,of the usual process, in whichsulphuric, acid is addedfto a massof dolomite, i. e., the presentinvention involves the progressive fractionaladditions'of the dolomiteto the diluted acid, instead of pouring the acid upon-the" dolomite.Furthermore, the

dolomite-HzSOeHzO reaction by the immediate use of the hot H2SO4-H2O,nevertheless a finely.

divided product may be obtained even if the heat of dilution andthat ofreaction is not utilized,

but a more fluffy product is obtained by the utilization of the heat ofdilution and that of reaction. Furthermore, a still more fiuffy type ofhydrated CaSO4 is obtained when external heat is used. In general, hightemperature-gives a flufiier material,

whereas lower temperatures give a material less fluffy. innature, and ithas been found that. the

to the H2SO4-H2O mixture under different tern-- 'more flufiy thematerial, the better it is adapted for use as aninsulating material. J I

The product obtained by adding the dolomite perature conditions willvary, for the'respective volume, weights approximately as follows:

' 1. The product obtained by-the addition of external heat to thediluted, acid and to'the reaction chamber during the progressive.addition of dolomite has a volume weight of approximately 2. The productobtained by the full usage of the heat generated by HZSOi-I-WfitGlsolution and jpOWder, unpacked. Eventhis last I mentioned 'productisdecidedly more'flufiy'than either the pulverized natural gypsum or thecrystalline product that is obtained bythe addition of. acid to thesolid carbonate; This will be appreciated when it is stated that theaddition'of concentrated 1 H2804 to a Mascotdolomite suspension in watergave a hydrated calcium sulphate weight of 29.6 pounds per cubic foot,while a 'commercialg'rade of "plaster of Paris weighed49.5 poundsper'cubic To recapitulatei By the use of the fundamental parting fromthe inventive idea.

the I dolomite being added .phuric-acidflvater solution and maintainingthe a still more fluffy product is obtained by the use of the heat ofdilution and that of reaction; while a still further fluffy type of thehydrated CaSOr nous, fluffy, pulverulent, crystalline, hydratedcalcium-sulphate, plus, of course, any insoluble is obtained whenexternal'heat is used.

While for the purpose of clearly describing the invention, specificproportions, temperatures and other features have been given, it will bereadily understood by those skilled in the art that these may bedeparted from withinlimits, without de- 7 I Furthermore while wehavespecifically describedthe inven- :tion in connection :with the use ofMascot dolomite, other forms of limestone may be simig .7 V, larlytreated, as well as natural carbonates, the It will be noted that theprocess of the present 1 amount employed in any case, however, beingslightly less than the --chemical equivalence of the sulphuric acidr Allof such ariations, aswell as such others as will readily suggestthemselves to those skilled in the art, as fall within the terms ofthearipended 'claims are intended to be covered thereby.

' Having thus described the invention, what is claimed is; i v

I 1. Aprocess comprising the step of adding dry dolomite to a hotsulphuric-acid-water mixture.

2. A process comprising the step of adding finely divided dry dolomitetoa hot sulphuric-acidwater mixture. s

3.'A process comprising the step of adding a fixed amount of drydolomiteto a hot-sulphuric- 1 acid-water solution, the, dolomite being added in,successive fractions 4. A process comprising the step of adding to a-hot sulphuric-aoid-water solution an amount of dry dolomite slightlylessthan the chemical equivalent of the sulphuricacid in said solution.

5. A process comprising the step of adding 1 o a hotsulphuric-acid-water solution an amount of dry dolomite slightly lessthan the chemical equivalent of the sulphuric acidin said'solution, 1

in successive fractions ofsaid amount. 1 6. A process comprising thestep of adding to a I hot sulphuric-acid-water solution amassof finelydivided dry dolomite, jsaid 'mass being slightly less than thechemicalequivalent of the sulphuric acid in said solution and being added insuccessivefractions of, said mass. 9.3 pounds per cubic footloosepowder, unpacked.

'7. A process comprising the step of adding in successive fractionsa drydolomite to a hot sulphuric-acid-watker solution and maintainingjthetemperature ofre'action heat approximately constant.

8. A process comprising the step of adding in successive fractions a drydolomite to a hot sultemperature ,of reaction heat at approximately 9. Aprocesscomprising the step of. adding in successive fractions adrydolomite to a hot sul-' 4 phuric-acid-water solutionwhile raising thetem- Zperature of the solution above that of the reaction heat. f

10.-A.process-comprising the step of forming a sulphuric-acid-Watersolutionypermittin'g the heat of reaction ofsaid solution to fall toroom "temperature, and then adding insuccessive fractions a dry dolomiteto the solution.

11. A processcomprising the step of adding dry dolomite to a hotsulphuric-acid-water solution and then repeatedly adding aquantity ofwater to the solution.

12. A process comprising thestep' of adding dry dolomite to a hotsulphuric-acid-water solu-- tion' and then repeatedly adding a :quantity.of water to the solution with gentle agitation after each addition ofwater.

.13. A process comprising the step', of adding dry dolomite to a hotsulphuric-acid-water solu-' tion and'then repeatedly "adding a quantityof water to the solution until the mass begins to contract.

14. A process comprising the steps of adding a dry dolomite to a hotsulphuric-acid-Water solu- 1 tion, then adding water to the-solution,then filtering out the resultant-hydrated calcium sulphate and washing,and drying thesa me 15. Aprocess comprising the steps of adding a massof dry dolomite to a hot sulphuric-acidwater solution, the said massbeing added in successive fractions thereof, then adding water to g thesolution, and then filtering out the resultant hydrated calciumsulphate. o i

16. A process comprisingthe steps of adding a mass of dry dolomite to ahot sulphuric-acidwater solution, the said mass being added in successive fractions thereof, then adding water to the to a hotsulphuric-acid-water solution and gently agitating to insure completehydration, and then adding water with L gentle agitation until the masscontracts sufiicientlyto show 'alayer of clear supernatantliquid, andthen filtering out the hydrated calcium sulphate.

, WALTER HO'GE MACINTIRE."

THOMAS BARNES STANSEL.

then washing and drying

